Tip:
Highlight text to annotate it
X
G'day, this is Dr Peter Price of Classroom Professor. Welcome to this week's video in
the Free Math Worksheet Series. This is week "28" and the strategy is "Difference of 1,
2 or 3". So this comes from our new book "Let's Go Book 4 Addition and Subtraction Revision".
Now this is a fairly challenging strategy for young students, older ones weren't having
trouble we would certainly hope, but the younger ones may have some difficulty with this. So
let's start with the question "11 - 8?" Now I'm saying "Minus" rather than "Take away"
deliberately because we're not taking away. We don't have a strategy where we're going
to count backwards by 8 or something like that, but we're looking at the two numbers
and comparing them. So with the 10 frame one approach to this will be say, put out 8 counters
and then we're going to see how many more there are in this amount here, this number
here. Make this up to 11, "How many more have we added?" And we're using a second colour
and of course we can see it's 3. Another way to do this, I'll change the question, so that
I can show it with the two 10 frame. Let's say "7 minus 4", we're comparing the 7 and
the 4, so we'll have 7 on this 10 frame and 4 on this one and you might prefer this, put
them next to each other, this might be clearer that way, here's 7, here's 4. "How many more
are there here?" So look at them visually, the students should be able to see the 4 at
this end and see there are 3 extra, so that's another way of using the 10 frames to see
the question. Using the number line it's simpler because, while we're counting back we're not
counting back this number, we're counting back until we get to that number. And so we're
looking, we're really looking at the difference of two numbers as the strategy indicates;
we're looking at really how far they are on the number line or the number of gaps between
then if you like. So if we start from the 7 and count back until we get to the 4, there's
the 4. "How many hops did we do backwards?" The answer is "3" so this must be the answer
to our question. As I've said it's a little bit tricky for the students so it will probably
take a bit of time to explain it to them. And that's it for this week's video; I'll
talk to you next time.